An opener of the type to which the present invention relates is shown in Gallis U.S. Pat. No. 3,890,744 wherein a patio door operating unit comprises a housing which mounts on the floor beside a fixed glass door next to a location that an adjacent sliding glass door occupies when the sliding glass door is in its open door position. Within the housing is an endless belt that engages the sliding door adjacent one end and that is driven along a horizontal path by an electric motor located within the housing. Electrical limit switches act to stop the door at its open and closed positions. The housing also includes a solenoid located adjacent the floor and connected to the motor circuit to tighten the belt when electric power is applied and to loosen it so the door can be moved by hand when power is off.
The Gallis device takes the form of a contained unit that can be readily mounted by a professional installer or homeowner-handyman after original installation of the doors. The unit includes an L-shaped bracket that is affixed at its top to the movable door through an opening in the part of the housing immediately adjacent the door and is clamped at its bottom to one run of the belt. Power is supplied to the unit by means of a standard cord that plugs into a nearby 110-volt power supply wall outlet. An operating switch is mounted at any convenient location on the wall adjacent the door opening and is connected to the rest of the circuitry by low voltage wiring.
The Gallis operator has all components, including the electric motor, control box and solenoid elements received within a uniform height, floor-mounted housing. This has several disadvantages. Such an arrangement requires that the housing have a corresponding minimum height to contain the same. This limits the location of the unit to a position, as shown in the '744 patent, that cannot extend very far beyond the fixed door panel. Positioning the same elsewhere would interfere with ingress and egress through the opening. Thus, while the Gallis operator may be suitable for patio door units having one opening and one fixed panel, the same would interfere with normal use of a patio door in which both door panels slide and would be unsuitable for larger openings having a greater number of sliding panels, such as openings in which a distal panel moves against one or more proximate panels to carry the proximate panels with it.
Even in use as an opener for a single sliding door adjacent a single fixed door, as disclosed in the '744 patent, the Gallis unit housing has an unsightly high profile. Gallis suggests that drapes may be hung and closed to conceal the housing; however, concealing the housing also obstructs the view through the fixed panel glass pane and frustrates a major purpose for having a see-through door in the first place.
The Gallis '744 unit is also deficient in that location of electrical elements along the floor in a housing having a slot facing the door exposes the electrical components to water due to rain and ground flooding. This is undesirable, particularly for ground level installations in low lying areas, and may even be impermissible under local electrical codes, particularly in the Southern States.
Moreover, though the opener of Gallis provides positive endless belt driven operation during door opening and closing, no suitable door movement locking mechanism is provided. When the belt-tightening solenoid of the preferred embodiment of the '744 patent is deenergized, the belt is slackened to present no impediment to manual movement of the sliding panel. The suggested alternative arrangement of locking the door by maintaining the power belt taut through continuous solenoid energization not only requires the steady costly application of energy with attendant additional wear on the active components, but is rendered useless whenever an electric power failure occurs. Also, where the solenoid is energized, manual override is impeded.